Changes in placental atrial natriuretic peptide receptors associated with severe toxemia of pregnancy.

We have previously demonstrated the presence of atrial natriuretic peptide (ANP) specific receptors in normal human placentas. Since toxemia of pregnancy may affect important metabolic, transport and hemodynamic functions of placentas, we have asked the question whether binding properties of human placental ANP receptors are changed in patients with severe toxemia of pregnancy when compared to normal patients. ANP receptors in plasma membranes from normal and severely toxemic patients were characterized by in vitro radioligand assays utilizing [125I]-alpha-hANP. In all cases, we identified specific, high affinity, low capacity ANP binding sites in a microsomal fraction of human placentas. Although the total concentration of receptors did not differ between the two groups, the dissociation constant, KD, was significantly higher in placentas from severely toxemic patients than from normal controls. From the above we conclude that placental ANP receptors are dynamically modulated and their characteristics may be altered in severe toxemia of pregnancy.